In order to elongate the lifetime of apparatuses arranged to form and record an image according to the electro-photographic method such as copying machines, laser printers, video printers, facsimile machines and their composite systems, a method in which the image on an image carrier is temporarily transferred to an intermediate transfer belt, and the transferred image is then fixed on a recording sheet has been investigated as an alternative to a method in which an image, composed of a recording material such as toner, formed on an image carrier such as a photosensitive drum is directly fixed to a recording sheet. Furthermore, a transfer method in which the recording sheet, on which the image is transferred, is conveyed has been investigated.
Hitherto, a semiconductive belt which can be used as the intermediate transfer belt is composed of a polyimide film containing an electrically conductive filler to have a volume resistivity of 1.sup.13 .OMEGA.cm to 10.sup.13 .OMEGA.cm as described in JP-A-5-77252 (the term "JP-A" as used herein means unexamined Japanese patent publication). The use of the polyimide film overcome problems of conventional semiconductive belts (JP-A-5-200904, JP-A-5-345368 and JP-A-6-95521) composed of a film made of vinylidene fluoride, ethylene-tetrafluoroethylene copolymer or polycarbonate, i.e., occurrence of a crack etc. at the end of the belt due to insufficient mechanical characteristics (e.g., strength and wear and abrasion resistance) and deformation of the transferred image caused by a load applied at driving.
However, the conventional semiconductive belts comprising the polyimide film are practically unsatisfactory in the environmental stability of the electric characteristics and durability. That is, the electric characteristics such as surface resistivity undesirably vary depending on external environment such as temperature and humidity. Furthermore, the electric characteristics largely vary with the long-term use. When the conventional semiconductive belt is used as the intermediate transfer belt or the transfer conveyance belt, there are problems such as transfer unevenness of the toner image transferred and developed on the recording sheet or separation failure of the recording sheet having an image transferred from the belt.